Current swimming fins are mainly categorized into full-foot swimming fins and adjustable strap-type swimming fins. Referring to FIG. 1 for a so-called full-foot swimming fin, a full-foot swimming fin 80 provides a shoe portion 81 having a fixed shoe size for a wearer to put on. However, the design of the shoe portion 81 is unfavorable for promptly putting on and removing for a wearer, and the fixed size of the shoe portion 81 also causes an associated developer and manufacturer to especially design a shoe shape or size for each wearer. In general, 6 to 9 differently-sized pairs need to be provided for every single style of the full-foot swimming fin 80 to accommodate the issue of different foot sizes of the public. More specifically, for the full-foot swimming fin 80, the 6 pairs mean that 6 pairs in different shoe sizes including XL, L, ML, M, S and XS need to be manufactured, and the 8 pairs mean that 9 pairs in different shoes sizes including XXXL, XXL, XL, L, ML, M, S, XS, and XXS need to be manufactured. As such, a developer and manufacturer needs to produce a predetermined number for each of the above sizes, which is equivalently producing large amounts of inventory that may be quite uneconomical. A distributor is also required to purchase stock of each of the above sizes for satisfy public needs, which again leads to large amounts of inventory. Further, the size of each full-foot swimming fin 80 is fixed, in a way that a rental provider is similarly required to prepare all of the sizes in order to cater the needs of all renting customers.
On the other hand, referring to FIG. 2 for an adjustable strap-type swimming fin, an adjustable strap-type swimming fin 90 is mainly formed by a webbed member 91 and a strap 92. The webbed member 91 provides a space 911 to be worn by only a front part of a human foot, and the strap 92 may be selectively connected to the webbed member 91. During the process of putting on, the front part of a foot of a wearer is placed in the space 911, and the strap 92 is wound around an ankle of the wearer to complete the process. Such method allows a wearer to adjust the size of the adjustable strap-type swimming fin 90. However, when the adjustable strap-type swimming fin 90 is put on, a heel of the wearer is unprotected by the adjustable strap-type swimming fin 90 and remains exposed. As a result, during scuba diving activities, the wearer may be easily cut but by external objects such as corals or reefs.